Search

Cs23Mn16O23 was synthesized via the azide/nitrate route from mixtures of Mn2O3, CsNO3, and CsN3. This manganese(II/III) mixed-valent oxide, which contains only one Mn3+ besides 15 Mn2+ cations, was studied by single-crystal X-ray diffraction and magnetic susceptibility measurements. Its crystal structure [P1, Z = 1, a = 1114.26(2), b = 1185.53(2), c = 1205.39(2) pm, α = 70.596(1), β = 80.377(2), γ = 83.072(2)°, R1 = 0.033] is based on a honeycomb-like arrangement of cesium atoms, providing the space for two different types of one-dimensional polyoxomanganate anions, illustrated by the syntax Cs23[MnO2]4[Mn3O5]4. Magnetic susceptibility measurements indicate dominant antiferromagnetic intra-chain interactions present already at ambient temperature and long range inter-chain magnetic ordering at 11 K.

In this work, we have successfully synthesized hollow microtubular crystals of the metal–organic framework (MOF) [Co2(NH2-bdc)2(dabco)]·[G] {G = H2O, N,N-dimethylformamide (DMF); NH2-bdc =2-amino-1,4-benzenedicarboxylate; dabco = 1,4-diazabicyclo[2.2.2]octane} by a very simple coordination-modulation method that avoids the use of an external modulator. Additionally, we have obtained the corresponding hollow microtubular crystals of Co3O4 through the solid-state thermolysis of the Co-MOF material at 400 °C. The as-prepared Co3O4 crystals exhibit the typical magnetic behavior for a nanostructured material with good crystallinity. Thus, this coordination-modulation method provides a simple route for the preparation of nanostructured porous frameworks and derived oxides and opens a way to prepare new materials with advanced properties.

The perovskite azido compound [(CH3)4N][Mn(N3)3], which undergoes a first-order phase change at Tt=310 K with an associated magnetic bistability, was revisited in the search for additional ferroic orders. The driving force for such structural transition is multifold and involves a peculiar cooperative rotation of the [MnN6] octahedral as well as order/disorder and off-center shifts of the [(CH3)4N]+ cations and bridging azide ligands, which also bend and change their coordination mode. According to DFT calculations the latter two give rise to the appearance of electric dipoles in the low-temperature (LT) polymorph, the polarization of which nevertheless cancels out due to their antiparallel alignment in the crystal. The conversion of this antiferroelectric phase to the paraelectric phase could be responsible for the experimental dielectric anomaly detected at 310 K. Additionally, the structural change involves a ferroelastic phase transition, whereby the LT polymorph exhibits an unusual and anisotropic thermal behavior. Hence, [(CH3)4N][Mn(N3)3] is a singular material in which three ferroic orders coexist even above room temperature. Triple-ferroic hybrid perovskite: The azido perovskite compound [(CH3)4N][Mn(N3)3] is a singular multiferroic material in which the three ferroic orders (electric, elastic, and magnetic) coexist even above room temperature (see figure).

The dielectric properties of mixed-oxide CaMn7O12 are reported. This compound exhibits a high dielectric constant at room temperature (er >1 0 4 ), for frequencies up to 10 4 Hz, values that make it very attractive for potential applications provided that its rather high losses can be minimized. Complex plane analysis of the obtained data reveal an important extrinsic contribution to these high er values; and also that the

Polycrystalline samples of the charge ordered mixed oxide LaMn0.5Co0.5O3−δ (TCO = 400 K) have been prepared by the nitrate decomposition method. These samples are biphasic, according to XRPD, and except one, oxygen defficient (δ ≈ 0.04-0.05). The study of the dielectric properties of these samples reveal that LaMn0.5Co0.5O3−δ displays a high dielectric constant, specially at room temperature and low frequencies. This e′r is seen to be strongly dependent on the particle size and not so much on the oxygen defficiency and the best properties are found in the sample with biggest particle size (ϕ = 7 μm) for which e′r (300 K) ≈ 105 up to 2x104 Hz. Analysis of the role of the grain size and the electrode contacts on the obtained data reveal that this mixed oxide has an intrinsic dielectric constant that is rather high for this type of compounds (e′r,∞ ≈ 30) and that is further enhanced by extrinsic Maxwell-Wagner effects. We relate such enhanced intrinsic dielectric constant to the electronic process of charge ordering present in this material below 400 K.

The title compound is synthesized by the azide/nitrate route from Mn2O3, CsNO3, and CsN3 (closed steel vessel, 773 K, 30 h) and characterized by powder and single crystal XRD, magnetic susceptibility measurements, and DFT calculations.

We report the structure and microstructure of the Ruddlesden-Popper (RP) series n=2 Gd2−2xSr1+2xCo2O7 (x = 0 and 0.10). X-ray powder diffraction, electron diffraction and HRTEM indicate that these compounds have a tetragonal structure (space group: P42/mnm) with cell parameters a ≈ 5.3749A c ≈ 19.3591A, in which the [CoO6] octahedra are distorted and tilted. Also, very interestingly, according to the obtained results these compounds presents A-site cation ordering where the divalent and bigger Sr2+ cation selectively prefers the 12-coordinated P site while the smaller and trivalent Gd3+ cation prefers the 9-coordinated R site. From the electrical point of view these materials are semiconducting and their resistivitiy decreases upon doping. In addition, the highest doped sample presents a small magnetoresistive effect MRmax = −3.2 % under Hmax = 50 kOe at T = 55 K.